1. Field of the Invention
This invention relates to a hermetic turbo-refrigerator apparatus mainly used with an air-conditioning system installed in a building.
2. Description of the Prior Art
The prior art documents published prior to the filing of the original application (priority date) include Japanese Patent Publication No. 21332/74 (inventor, Shoji Ichikawa), Japanese Patent Publication No. 18942/77 (inventors, Akiichi Takata et al) and U.S. Ser. No. 937,806, now U.S. Pat. No. 4,295,792.
Japanese Patent Publication No. 21332/74 discloses a turbo-refrigerator apparatus comprising a turbocompressor, a motor for driving the turbocompressor, a condenser, a pressure-reducing valve, an evaporator and suction vanes, wherein the drive motor is in the form of a high-speed DC motor or a thyristor motor, and speed control means, such as resistance control means or thyristor chopper control means, is mounted between the motor and a DC power source. While operating in a cooling mode, an impeller of the turbocompressor has its number of revolutions controlled in such a manner that the number of revolutions is commensurate with the difference in temperature between brine at the outlet of the evaporator and cooling water at the inlet of the condenser. By controlling the number of revolutions of the impeller of the turbocompressor by following up differences in temperature between the cooling water and brine or changes in the temperature of cooling water as disclosed in this prior art document, it would be possible to minimize an input of power and to operate the turbocompressor at a low energy consumption level.
However, the use of a high-speed DC electric motor as a drive motor, a DC power source as a power source and resistance control means or thyristor chopper control means as speed control means involves an increase in capital cost because the equipment is complex in construction and large in size. Since the ordinary power source commercially available is an AC power source, it is necessary to use a DC-AC converter (electricaly operated DC generator) to provide a DC power source. This is one of the factors concerned in increased capital cost.
Disclosed in Japanese Patent Publication No. 18942/77 is a turbo-refrigerator apparatus comprising a turbocompressor, a prime mover, a condenser and a cooler, wherein speed regulating means for the prime mover and detector means for detecting the flow rate and temperature of cooling fluid in the condenser or the internal pressure of condenser are provided, the speed regulating means being controlled in accordance with the values detected by the detector means to thereby control the number of revolutions of the impeller of the turbocompessor. This prior art could achieve the same results as those achieved by Japanese Patent Publication No. 21332/74.
However, in Japanese Patent Publication No. 18942/77, it is stated that the prime mover may be in the form of a steam turbine or a high frequency electric motor. Thus an increase in capital cost could not be avoided whichever of the two might be selected. Generally, a steam turbine is low in efficiency, so that a system including the steam turbine would be low in efficiency as a whole even if the efficiency of the turbocompressor were increased by effecting control of the number of revolutions of its impeller.
In U.S. Pat. No. 4,295,792 a device for controlling operation of a fluid pressure raising system is proposed which includes at least a centrifugal compressor, a speed increasing gear system, an electric motor of constant speed and a detector for detecting atmospheric conditions or a discharge pressure, such device being operative to change the speed increase ratio of the speed increasing gear system in accordance with the value detected by the detector in controlling the number of revolutions of the impeller of the centrifugal compressor, to thereby increase the efficiency of the centrifugal compressor. The invention disclosed in the aforementioned U.S. patent offers the advantage that the capital cost is low because the equipment is simple in construction inasmuch as the number of revolutions of the impeller is controlled by the speed increasing gear system. However, since the centrifugal compressor, speed increasing gear system and electric motor are mounted independently of one another in open-type equipment, a difficulty would be encounted in providing a seal to portions of the housing through which the impeller shaft extends. Particularly, when the equipment in which the device is incorporated is a refrigerator apparatus, it is essential that no working fluid or a refrigerant, which generally belongs to a group of refrigerants bearing the name of Freon (trade name), be allowed to leak from the equipment. Thus, U.S. Pat. No. 4,295,792 would require an improvement for providing a satisfactory seal to the housing.